A plurality of communication systems are included in mobile communications as represented by a cellular telephone. For example, in Europe, there exists W-CDMA as a third generation communication system that has recently started its service in addition to GSM prevalent as a second generation communication system, and EDGE at a transmission rate enhanced from that of GSM data communications. Further, in North America, cdma 1x as a third generation communication system is prevalent in addition to DCS, and PCS, as a second generation communication system. Incidentally, GSM stands for Global System for Mobile Communications. EDGE stands for Enhanced Data rate for GSM Evolution. W-CDMA stands for Wide-band Code Division Multiple Access. DCS stands for Digital Cellular System. PCS stands for Personal Communications System, and cdma 1x stands for Code Division Multiple Access 1x. 
In Non-patent document 1 described hereunder, it is described that a matching technology with the use of a transmission line transformer (TLT: Transmission Line Transformer) is used in multi-octave impedance conversion by an RF wave, and a low-end microwave. With a conventional power amplifier, a multitude of inductors, capacitors, and transmission lines, or combinations thereof are generally used in a ladder circuit in order to implement a transformer for converting an ultra-low impedance to 50 Ω in a band of an octave, or more. In the case of a traditional technology using those constituents, the power amplifier has a limited frequency band, and is lager in circuit size. A transmission line transformer (TLT) using a straight line section, or a coil section of the transmission line as coupled will have a broadband, and be smaller in circuit size. Further, in the Non-patent document 1 described hereunder, it is also described that this type of the transformer can be designed to enable application of a multi-level interconnection manufacturing technology to any of, for example, a printed wiring board, low temperature calcined ceramics (LTCC), high temperature calcined ceramics (HTCC), a monolithic silicon (Si) IC, and a gallium arsenide (GaAs) IC.
In Non-patent document 2 described hereunder, a Guanella type transmission line transformer (TLT), and a Ruthroff type transmission line transformer (TLT) are introduced, and it is further described that a non-equilibrium Guanella type transmission line transformer (TLT) is formed by use of three-layer interconnections provided on a GaAs substrate.
In Non-patent document 3 described hereunder, it is described that in contrast to a conventional transformer functioning by coupling of magnetic fluxes, a transmission line transformer (TLT) differs from the former in that energy is transmitted to an output circuit in a transmission line mode. In general, floating inductance and parasitic capacitance are absorbed by a characteristic impedance of a transmission line, so that the transmission line transformer (TLT) is considered to end up indicating a broader frequency band, and higher efficiency than in the case of the conventional transformer. An off-chip transmission line transformer (TLT) is in use for conversion of a single-end signal to a differential signal by use of a low noise amplifier (LNA) for application of 2.4 GHz Bluetooth, or reverse conversion thereof.
In Non-patent document 4 described hereunder, it is described that while internal interconnection capacitance must be taken into consideration in a frequency band of 2 to 30 MHz although a transformer is a useful constituent for impedance matching, the Guanella type transmission line transformer (TLT), and the Ruthroff type transmission line transformer (TLT) are useful at a phenomenally large power level, and can be configured with ease, being inexpensive, and light in weight, thereby enabling a broader band to be used. With a broadband high-output RF linear amplifier in the frequency band of 2 to 30 MHz, for use in SSB and AM communications, a transmission line transformer (TLT) wound around a ferrite toroid is used between stages of a multistage amplifier, and in an output matching circuit.
Further, in Non-patent document 5 described hereunder, there is described use of choke inductance as a load of a power amplifier for RF communications, of which high efficiency is required. In the Non-patent document 5, it is also described that the choke inductance can check harmonics of current fed from a DC power supply to the amplifier.
[Non-Patent Document 1]
    Inder J. Bahl, “Broadband and Compact Impedance Transformer for Microwave Circuits”, IEEE MCROWAVE magazine, pp. 56-62, August, 2006.[Non-Patent Document 2]    J. Horn, et al., “Integrated Transmission Line Transformer”, 2004 IEEE MTT-S Digest, pp. 201-204[Non-Patent Document 3]    Bill Toole, et al., “A Low Voltage, Low Power RF CMOS LNA for Bluetooth Applications using Transmission Line Transformers”, Proceedings of the 27th European Solid—State Circuits Conference, 2001, ESSCIRC, 18-20 Sep. 2001, pp. 433-436[Non-Patent Document 4]    OCTAVIUS PITZALIS, et al., “Broadband 60—W HF Linear Amplifier” IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-6, NO. 3, June 1971, pp. 93-103[Non-Patent Document 5]    Brett E. Klehn, et al., “AN EXACT ANALYSIS OF CLASS—E POWER AMPLIFIERS FOR RF COMMUNIATIONS”, Proceedings of the 2004 International Symposium on Circuits and Systems, pp. 277-280